I have already observed,[3] in examining the foundation of mathematics, that the imagination, when set into any train of thinking, is apt to continue even when its object fails it, and, like a galley put in motion by the oars, carries on its course without any new impulse. This I have assigned for the reason, why, after considering several loose standards of equality, and correcting them by each other, we proceed to imagine so correct and exact a standard of that relation as is not liable to the least error or variation. The same principle makes us easily entertain this opinion of the continued existence of body. Objects have a certain coherence even as they appear to our senses; but this coherence is much greater and more uniform if we suppose the objects to have a continued existence; and as the mind is once in the train of observing an uniformity among objects, it naturally continues till it renders the uniformity as complete as possible. The simple supposition of their continued existence suffices for this purpose, and gives us a notion of a much greater regularity among objects, than what they have when we look no farther than our senses. But whatever force we may ascribe to this principle, I am afraid 'tis too weak to support alone so vast an edifice as is that of the continued existence of all external bodies; and that we must join the _constancy_ of their appearance to the _coherence_, in order to give a satisfactory account of that opinion. As the explication of this will lead me into a considerable compass of very profound reasoning, I think it proper, in order to avoid confusion, to give a short sketch or abridgment of my system, and afterwards draw out all its parts in their full compass. This inference from the constancy of our perceptions, like the precedent from their coherence, gives rise to the opinion of the _continued_ existence of body, which is prior to that of its _distinct_ existence, and produces that latter principle.